1. Field of the Invention
The present invention provides a method of producing a polyolefin composition comprising contacting a metallocene pre-catalyst, a co-catalyst, a primary surrogate, and a secondary surrogate; adding a first olefin monomer; and polymerizing the first monomer for a time sufficient to form the polyolefin. The present invention also provides a method of producing a block polyolefin composition comprising contacting a metallocene pre-catalyst, a co-catalyst, a primary surrogate, and a secondary surrogate; polymerizing the first monomer for a time sufficient to form the polyolefin; adding a second monomer; and polymerizing the second olefin monomer for a time sufficient to form said block polyolefin composition. The method allows for the production of polyolefins of low molecular weights and narrow molecular weight distributions.
2. Related Art
Several transition-metal-based catalysts have been reported that can mediate the living metal-mediated coordination polymerization (also known as homogeneous, single-site Ziegler-Natta polymerization) of ethene, propene, higher α-olefins, and α,ω-nonconjugated dienes, and, in some cases, these proceed with a high degree of stereocontrol (tacticity) ((for a review of catalysts for living coordination polymerization of ethene and α-olefins, see: Coates, G. W., et al., Angew. Chem. Int. Ed. 41:2236-2257 (2002)); (for the living and stereoselective coordination polymerization of α-olefins and α,ω-non-conjugated dienes, see: Jayaratne, K. C., et al., J. Am. Chem. Soc. 122:958-959 (2000)); Jayaratne, K. C., et al., J. Am. Chem. Soc. 122:10490-10491 (2000); Keaton, R. J., et al., J. Am. Chem. Soc. 123:6197-6198 (2001); Zhang, Y., et al., Chem. Commun. 2358-2359 (2003); Zhang, Y., et al., Organometallics 23:3512-3520 (2004); Harney, M. B., et al., Angew. Chem. Int. Ed. 45:2400-2404 (2006); Harney, M. B., et al., Angew. Chem. Int. Ed. 45:6140-6144 (2006); Zhang, W., et al., Adv. Synth. Catal. 350:439-447 (2008)). However, the commercialization of new polyolefin materials and products that take advantage of the unique capabilities of living coordination polymerizations appears unlikely ((for reviews of polyolefin materials prepared through living coordination polymerization, see: Domski, G. J., et al., Prog. Polym. Sci. 32:30-92 (2007); Sakuma, A., et al., Polym. J. 39:193-207 (2007)); Szwarc, M., et al., Ionic Polymerization and Living Polymers; Chapman & Hall: New York (1993); Quirk, R. P., et al., Polym. Int. 27:359-367 (1992); Matyjaszewski, K., J. Phys. Org. Chem. 8:197-207 (1995)).
The same fundamental criterion of a living polymerization, namely, chain-growth propagation in the absence of irreversible chain termination, serves to establish a ‘one polymer chain per active metal center’ cap on product yield as a critical liability. The severity of this liability sharply increases as the targeted number-average degree of polymerization, Xn, of the desired polyolefin product decreases. While living coordination polymerization is ideally suited for accessing the largely unexplored material science and technology associated with architecturally well-structured ‘precision polyolefins’ of very low to moderate molecular weights (ca 500-10,000 Da), the practical availability of significant quantities of these materials presently remains out of reach due to unfavorable weight (polymer) to weight (catalyst) ratios ((for a review of catalysts for living coordination polymerization of ethene and α-olefins, see Coates, G. W., et al., Angew. Chem. Int. Ed. 41:2236-2257 (2002)); (for reviews of polyolefin materials prepared through living coordination polymerization, see Domski, G. J., et al., Prog. Polym. Sci. 32:30-92 (2007); Sakuma, A., et al., Polym. J. 39:193-207 (2007)); Szwarc, M., et al., Ionic Polymerization and Living Polymers; Chapman & Hall: New York (1993); Quirk, R. P., et al., Polym. Int. 27:359-367 (1992); Matyjaszewski, K., J. Phys. Org. Chem. 8:197-207 (1995); Kaneyoshi, H., et al., Macromolecules 38:5425-5435 (2005); Ring, J. O., et al., Macromol. Chem. Phys. 208:896-902 (2007); Ventold, L., et al., J. Phys. Chem. Solids 66:1668-1674 (2005)).
International Application Publication No. WO 2009/061499 discloses the living coordinative chain-transfer polymerization and copolymerization of ethene, propene, long-chain α-olefins, and α,ω-nonconjugated dienes using {η5-C5Me5)Hf(Me)[N(Et)C(Me)N(Et)]}[B(C6F5)4] as the active transition-metal initiator for chain-growth propagation with multiple stoichiometric equivalents of diethylzinc (ZnEt2) as surrogate chain growth sites. Successful living coordinative chain-transfer polymerization of these monomers requires that the rate, and rate constant for reversible (polymeryl group) chain transfer between the active transition-metal propagating centers and the inactive surrogate main-group metal species, vct and kct, respectively, should be far greater than the corresponding kinetic parameters for transition-metal-mediated propagation, vp and kp, in order to insure that all active and surrogate species appear to propagate at the same rate.
The final yield of polyolefin product obtained through living coordinative chain-transfer polymerization is dependent only upon the initial volume of ZnEt2 employed. Thus, living coordinative chain-transfer polymerization circumvents the “one-polymer-per-metal-center” criterion of traditional living coordination polymerizations that has proven to be an insurmountable liability to scalable production of precision polyolefins and precision hydrocarbons. However, from a cost and safety perspective, the transport and handling of industrial volumes of ZnEt2 is problematic and accordingly, the dependence of a living coordinative chain-transfer polymerization method on ZnEt2 may limit the commercialization of precision hydrocarbons and precision-hydrocarbon based products. Conversely, AlEt3 and Al(iso-butyl)3 can be produced on a commodity scale from aluminum powder, dihydrogen, and ethene or isobutene, respectively, and are significantly less expensive and substantially less pyrophoric in contact with air than ZnEt2. Furthermore, if all three alkyl groups of these trialkylaluminums engage equally in rapid in reversible chain-transfer, trialkylaluminums have an additional advantage over ZnEt2.
In 1952, Karl Ziegler introduced the Aufbaureaktion, a process by which the controlled oligomerization of ethene can be achieved using triethylaluminum, AlEt3, as a chain-growth initiator at high pressure (about 100 psi) and at low temperatures (about 130° C.) (Ziegler, K., Angew. Chemie 64:323-329 (1952)). The process was commercially successful due to its ability to provide a pseudo-Poisson distribution of long-chain linear α-olefins of general formula H2C═C(C1-2)nCH3 (n=1-15) and the corresponding saturated terminal alcohols, HOCH2(CH2)n+1CH3, through direct chemical transformations of Al[(CH2)n+2CH3]3 intermediates. In 2006, global production of long-chain linear α-olefins was four million metric tons, with 55% of this amount targeted for lubricants, plasticizers, detergents, additives, and fine chemicals. However, no Aufbaureaktion for the controlled oligomerization of propene or long chain α-olefins using AlEt3 or other trialkylaluminums as a chain-growth initiator has been developed. Accordingly, the potential technological value of new classes of hydrocarbon-based products that might be available from such processes on a commodity volume scale remains unknown.
Precision hydrocarbons represent a new class of polyolefins that are distinguished by having programmable and architecturally-discrete carbon-carbon bonded frameworks, very low (e.g., oligomeric) molecular weights, and extremely narrow molecular weight distributions. It is believed that precision hydrocarbons could offer benefits to society as green and sustainable synthetic base stock oils and waxes for a broad range of technological applications.
It should be noted that it was not obvious that ZnEt2 could be used to realize the goal of ternary living coordinative chain-transfer polymerization. It has previously been reported that, in solution, a 1:1 mixture of AlEt3 and ZnEt2 undergoes spontaneous decomposition to yield unindentifiable products (Périn, S. G. M., et al., Macromol. Chem. Phys. 207:50-56 (2006)). Additionally, the use of ZnEt2 as both a secondary surrogate and as a chain-transfer mediator is mechanistically quite distinct from its role as a chain-shuttling agent for transfering a polymeryl group between two different active transition-metal propagating species as originally used for the production of blocky poly(ethene-co-octene) via a non-living process (Hustad, P. D., et al., Macromolecules 40:7061-7064 (2007)). It is believed that the use of two different main-group metal alkyl species that play different synergistic roles within the coordinative chain transfer polymerization of ethene, propene, or longer-chain α-olefins has not yet been reported.
There is a need, therefore, for new methods of coordination polymerization of olefins that allows for scalability of the volume of polyolefins that can be prepared through living polymerization with a dramatic reduction in the amount of transition metal catalyst that is required while not sacrificing all the desired beneficial features of the polymer that can be obtained through a living process, including tunable molecular weights, narrow polydispersities, ability to prepare block copolymers with discrete block junctions, random copolymers, and polyolefins with well-defined and discrete end-group functionalizations.